Trends in the electric power utility automation sector, specifically substation automation, have been driving towards common communications architecture. The initiative was begun in the early 1990s driven by the major North American utilities under the technical auspices of Electric Power Research Institute (EPRI). The resulting standard that emerged is known as the Utility Communications Architecture 2.0 (UCA2). At the heart of this architecture is the substation LAN (Local Area Network) based on Ethernet. However, one of the major requirements for electronic devices used in substations as part of a protection and control system is their ability to operate reliably in harsh environmental conditions. Harsh environmental conditions include conditions having both adverse atmospheric conditions and adverse electrical conditions. Substation environments are much harsher than the office environments where the overwhelmingly majority of Ethernet equipment resides and was designed for.
It would therefore be desirable for the Ethernet switch, which forms the backbone of the substation LAN, to be as reliable and robust as other IEDs (Intelligent Electronic Devices) designed specifically to operate in harsh substation environments. One such group of IEDs are protective relays which perform the function of protecting the power system from ault conditions and other anomalies. Modern, microprocessor based protective relays are adhering to the UCA2 standard and providing one or multiple Ethernet ports ready to connect to suitable Ethernet Switches.
However, the prior art Ethernet switches do not meet these standards. In particular, the prior art switches do not adhere to the ANSI/IEEE C37.90 standard (US) and the IEC-60255 standard (Europe) which were designed for protective relaying IEDs and other intelligent devices found in electrical substations. For example, the prior art devices do not satisfy at least the following criteria.
(A) Electrical Environment
                1. Surge Withstand Capability as per ANSI/IEEE C37.90.1 (1989), namely withstanding 2.5 k Voscillatory transients, 4.0 kV fast transients applied directly across ach output, input and power supply circuit.        2. Surge Immunity as per IEC 61000-4-5 (1995 Level 4) standards.        3. High Frequency Noise Disturbance as per IEC 60255-22-1 (1988 Class III) standards.        4. Fast Transient Disturbance as per IEC 60255-22-4 (1992 Class IV) standards, namely withstanding 4 kV, 2.5 kHz applied directly to the power supply inputs and 4 kV, 2.5 kHz applied directly to all other inputs.        5. Dielectric Withstand as per ANSI/IEEE C37.90-1989 and IEC 60255-5: 1977 standards.        6. High Voltage Impulse Test as per IEC 60255-5: 1977 standard.        7. Electrostatic Discharge as per IEC 60255-22-2: 1996 Class 4 and Class 3 standards.        8. Radiated Radio Frequency Immunity as per IEEE C37.90.2 and IEC 61000-4-3 standards.(B) Atmospheric Environment        1. Temperature: Cold at −40° C. as per the IEC 60068-2-1 standard and dry heat at 85° C. as per IEC 60068-2-2 standard.        2. Temperature Cyclic: −25° C. to +55° C. as per IEC 60255-6 (1998) standard.        3. Relative Humidity: 5 to 95% as per the IEC 60068-2-2 standard.        
Referring now to FIG. 1, an electronic circuit block diagram, shown generally by reference numeral 10 of a conventional commercial Ethernet Switch is shown. The circuit 10 consists of an Ethernet Media Access Controller (MAC) block 1 which typically provides a plurality of communications ports each adhering to the Reduced Media Independent Interfaces (RMII) signaling specification as put forth by the version 1.2 of the RMII Consortium. These RMII ports interface to a physical layer device 4, referred to as a PHY, which converts the RMII signals to differential transmit and receive signal pairs in accordance with the IEEE 802.3 10BaseT and or 100BaseTX standards. These signals are then noise filtered by the filter block 5a and electrically isolated via pulse transformers 5b which also couple the signals to the RJ45 style connector receptacles 5c which are typical of commercial grade Ethernet Switches. The RJ45 interface 8 typically accepts TIA/EIA 568 category 5 (CAT-5) unshielded twisted pair copper wire cables. Power is typically provided by a single power supply block 6 and cooling of the electronics is also typically provided by a low-voltage DC powered cooling fan 7 typical of those found in personal computers.
The electronic circuit 10 illustrated in FIG. 1 has numerous shortcomings when used in a utility substation environment. In particular the switch is susceptible to electrical transients and electromagnetic interference being coupled into the device via twisted pair copper cables 8. This is extremely undesirable since it could result in corruption of real-time mission critical control messages being transmitted over the network via the switch. Moreover, actual damage to the switch itself is possible if high voltage electrical transients are directly coupled into the device via the copper cables overcoming the limited electrical isolation (typically 1500V RMS) provided by isolation transformers 5b. Another point of electrical transient susceptibility in the design of FIG. 1 is the power supply input 6a. The power supply block 6 must be capable of enduring electrical transients at levels of 2 kV to 5 kV as specified by the ANSI/IEEE C37.90 and IEC 60255 standards. This is not a requirement for commercial grade Ethernet Switches and thus the power supply inputs 6a do not provide suitable transient suppression circuitry. Furthermore, commercial grade Ethernet switches are not specifically designed to withstand EMI (Electromagnetic Interference) levels of 35V/m as specified by ANSI/IEEE C37.90.2 (1995) which is typical or the substation environment.
Accordingly, conventional circuit 10 suffers from the disadvantage that it is susceptible to electrical transients and electromagnetic interference at levels which are possible, or even common, in utility substation environment. The design of FIG. 1 is also susceptible to mechanical breakdown because of the use of rotating cooling fan 7 required to cool the electronic components. Thus the reliability of the Ethernet Switch is determined by the reliability of the fan which is the only moving mechanical part in the design and typically has the lowest Mean-Time-Between-Failures (MTBF) value, such as less than 10,000 Hrs, compared to electronic components which have MTBF values of greater than 450,000 Hrs. It would be highly desirable to eliminate the fan block 7 from the design and improve the reliability of the Ethernet Switch to MTBF levels similar to those of the IEDs, which would be connected to it, namely greater than 450,000 Hrs. Furthermore, the typical operating temperature range of commercial Ethernet Switches having the circuit 10 shown in FIG. 1. is 0° C. to 40° C. (ambient) with fan cooling 7. However, the operating temperature range for devices in the substation environment such as protective relays is specified by the IEC 60255-6 (1998) standard as −25° C. to +55° C. Therefore, not only is the circuit 10 of FIG. 1 susceptible to failure, it also does not meet the requirements of the environmental conditions which are possible, or even common in utility substation environments.
Furthermore, because of the mission critical nature of the application, that being the use of the substation LAN to send real-time control messages during power system fault conditions, the availability or “up time” of the Ethernet Switch is critical to proper operation of the protection and control system. A further point of susceptibility of the design of FIG. 1 is the power supply block 6. If the power supply block 6 fails then the Ethernet Switch fails and is not available to provide the backbone of the LAN during the critical period of time where the protection and control system needs to respond in the order 4 to 100 ms. Accordingly, there is a need in die art for an Ethernet Switch having redundant, parallel power supply blocks such that if one failed the other would continue to supply the required regulated power to the Ethernet Switch without any interruption to its operation.